1. Field of the Invention
The present invention relates to a projection display apparatus utilizing a red component light, a green component light, a blue component light, and additionally, a fourth color component light.
2. Description of the Related Art
Conventionally, there has been known a projection display apparatus including three imagers for lights of three colors, a cross dichroic cube for combining lights emitted from the three imagers, and projection unit for projecting the lights combined by the cross dichroic cube.
Here, the cross dichroic cube has three light incidence surfaces which lights respectively enter, and one light emitting surface from which the lights exit. Therefore, one cross dichroic cube is enough for the projection display apparatus if lights entering the cross dichroic cube are of three colors.
Meanwhile, a projection display apparatus utilizing lights of four or more colors has been proposed for the purpose of improving color reproducibility or luminance. For example, one projection display apparatus utilizes orange, yellow or cyan in addition to three colors of red, green, and blue so as to improve color reproducibility or luminance (see Japanese Patent Publication No. 2002-287247, for example).
Here, when a projection display apparatus utilizes lights of four or more colors, only one cross dichroic cube cannot combine the lights of four or more colors. Hence, the projection display apparatus needs to have two or more dichiroic cubes (or cross dichroic cubes).
For example, when lights of four colors are needed to be combined, a projection display apparatus firstly acquires two combined lights, each of which is formed by combining lights of two colors, and then combines the two combined lights to acquire a combined light of four colors. Alternatively, the projection display apparatus may acquire a combined light of four colors by acquiring a combined light of three colors, and combining the combined light with a light of one color. The projection display apparatus may also acquire a combined light of four colors by acquiring a combined light of two colors, and combining the combined light with lights of the other two colors.
In these cases, two or more dichroic cubes (or cross dichroic cubes) need to be provided between imagers and projection unit. This makes the back focus of the projection unit longer.
As a result of this, since projection unit used in a projection display apparatus utilizing lights of three colors cannot be used for another type of projection display apparatus, cost of the projection display apparatus as a whole rises.